[PATCH RFC v5 2/3] iomap: use BIO_COMPLETE_IN_TASK for dropbehind writeback

Tal Zussman
2026-04-08T23:09:10Z

Set BIO_COMPLETE_IN_TASK on iomap writeback bios when a dropbehind folio
is added. This ensures that bi_end_io runs in task context, where
folio_end_dropbehind() can safely invalidate folios.

With the bio layer now handling task-context deferral generically,
IOMAP_IOEND_DONTCACHE is no longer needed, as XFS no longer needs to
route DONTCACHE ioends through its completion workqueue. Remove the flag
and its NOMERGE entry.

Without the NOMERGE, regular I/Os that get merged with a dropbehind
folio will also have their completion deferred to task context.

Signed-off-by: Tal Zussman <tz2294@columbia.edu>
---
fs/iomap/ioend.c | 5 +++--
fs/xfs/xfs_aops.c | 4 ----
include/linux/iomap.h | 6 +-----
3 files changed, 4 insertions(+), 11 deletions(-)

diff --git a/fs/iomap/ioend.c b/fs/iomap/ioend.c
index e4d57cb969f1..fe2a4c3dae42 100644
--- a/fs/iomap/ioend.c
+++ b/fs/iomap/ioend.c
@@ -182,8 +182,6 @@ ssize_t iomap_add_to_ioend(struct iomap_writepage_ctx *wpc, struct folio *folio,
ioend_flags |= IOMAP_IOEND_UNWRITTEN;
if (wpc->iomap.flags & IOMAP_F_SHARED)
ioend_flags |= IOMAP_IOEND_SHARED;
- if (folio_test_dropbehind(folio))
- ioend_flags |= IOMAP_IOEND_DONTCACHE;
if (pos == wpc->iomap.offset && (wpc->iomap.flags & IOMAP_F_BOUNDARY))
ioend_flags |= IOMAP_IOEND_BOUNDARY;

@@ -200,6 +198,9 @@ ssize_t iomap_add_to_ioend(struct iomap_writepage_ctx *wpc, struct folio *folio,
if (!bio_add_folio(&ioend->io_bio, folio, map_len, poff))
goto new_ioend;

+ if (folio_test_dropbehind(folio))
+ bio_set_flag(&ioend->io_bio, BIO_COMPLETE_IN_TASK);
+
/*
* Clamp io_offset and io_size to the incore EOF so that ondisk
* file size updates in the ioend completion are byte-accurate.
diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 76678814f46f..0d469b91377d 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -510,10 +510,6 @@ xfs_ioend_needs_wq_completion(
if (ioend->io_flags & (IOMAP_IOEND_UNWRITTEN | IOMAP_IOEND_SHARED))
return true;

- /* Page cache invalidation cannot be done in irq context. */
- if (ioend->io_flags & IOMAP_IOEND_DONTCACHE)
- return true;
-
return false;
}

diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 99b7209dabd7..a5d6401ebd80 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -392,16 +392,12 @@ sector_t iomap_bmap(struct address_space *mapping, sector_t bno,
#define IOMAP_IOEND_BOUNDARY (1U << 2)
/* is direct I/O */
#define IOMAP_IOEND_DIRECT (1U << 3)
-/* is DONTCACHE I/O */
-#define IOMAP_IOEND_DONTCACHE (1U << 4)
-
/*
* Flags that if set on either ioend prevent the merge of two ioends.
* (IOMAP_IOEND_BOUNDARY also prevents merges, but only one-way)
*/
#define IOMAP_IOEND_NOMERGE_FLAGS \
- (IOMAP_IOEND_SHARED | IOMAP_IOEND_UNWRITTEN | IOMAP_IOEND_DIRECT | \
- IOMAP_IOEND_DONTCACHE)
+ (IOMAP_IOEND_SHARED | IOMAP_IOEND_UNWRITTEN | IOMAP_IOEND_DIRECT)

/*
* Structure for writeback I/O completions.

--
2.39.5